High-latitude vegetation dynamics : 850 years of vegetation development on Mt Hekla, Iceland

• Main Author: Cutler, Nick
• Other Authors: Belyea, Lisa. : Dugmore, Andy
• Published: University of Edinburgh 2008
• Subjects: 580.9; geography
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.562149

The overall aim of this thesis is to investigate long-term (multi-century) vegetation development in a high-latitude setting, with a particular emphasis on the emergence and persistence of spatial structure in plant communities. The spatial distribution of plants within a community influences vegetation dynamics and the functioning of terrestrial ecosystems. Knowledge of the spatiotemporal dynamics of vegetation is therefore crucial to understanding ecosystem response to disturbance, and to successful ecosystem management. Studies of spatiotemporal dynamics from high-latitude settings are rare, despite these regions being among the most sensitive to warming and subject to ongoing environmental change. The study was based on a primary succession on Mt Hekla in south-central Iceland. The chronosequence approach was used to infer 850 years of vegetation development from a suite of 14 lava flows (five of which had been disturbed by the deposition of volcanic tephra). The thesis is organised around four main research themes: 1) Trajectories of development- How do the global (i.e. non-spatial) properties of a community (e.g. species diversity) change with terrain age in a primary succession? Plant species frequency data from 12 transect surveys (each comprising 400 contiguous 10 cm x 10 cm quadrats) were used to test the predictions of classical models of primary succession; 2) Initial colonisation- How do plants first establish on newly-created terrain? Photographic surveys and point-pattern analysis were used to assess the processes by which pioneer species colonised ‘safe sites’ on lava surfaces six and fifteen years old; 3) Spatial scale and structure- How and why does the spatial structure of vegetation vary over long timescales? Vegetation and soil data from transect surveys (item 1, above) were analysed using a variety of spatial statistics, in order to test three models of spatiotemporal dynamics; 4) Temporal changes in environmental gradients- To what extent does biotic reaction feed-back into the small- (metre-) scale distribution of plants? Randomised sampling of vegetation on 42 sites was combined with continuous microclimatic monitoring to assess the changing steepness of environmental gradients, and the impact this process had on vegetation development. The analyses revealed a robust, multi-century trajectory of vegetation development on undisturbed sites. The development of vegetation on newly-emplaced flows was rapid, as colonists randomly exploited small- (millimetre) scale surface irregularities in the lava. A thick (up to 20 cm), spatially homogeneous ‘carpet’ of moss formed within 50 years of flow emplacement. Thereafter, the vegetation became progressively more structured with increasing terrain age, as patches of vegetation formed and expanded. On the oldest sites, differentiation of the vegetation according to metre-scale variations in elevation was apparent. Overall, the results emphasise the limitations of classical models of succession in high-latitude habitats and suggest widespread applicability for the nucleation model of primary succession. The study also suggests that the spatiotemporal response of vegetation to environmental gradients is mediated by short-range positive feedback. These findings have implications for modelling vegetation development on other primary substrates (e.g. glacial forelands) and the response of spatially patchy, high-latitude vegetation to future climate change.